1. Field of the Invention
The present invention relates to a technology for recording information onto an information recording medium such as an optical disc.
2. Related Art
In recent years, attention has been paid to an optical disc such as a DVD-RAM as a large capacity information recording medium, and the optical disc has been developed and merchandised for an external memory of a computer and for picture and voice recording. In general, the optical disc is provided with a spiral or concentric track on a disc surface and laser beams are irradiated along the track, thereby recording and reproducing information. Moreover, the track is further divided into a plurality of sectors which become the minimum unit for recording and reproducing information data.
As a method for recording information onto the optical disc, there has generally been known a light modulation recording method for modulating the intensity of a laser beam irradiated on the track onto which data are to be recorded according to the data to be recorded. Typically, there have been known recording methods applicable to an optical disc material over a wide range, for example, a phase change type optical disc, an organic pigment type optical disc, a magnetoxe2x80x94optical disc and the like.
Moreover, a pulse width modulation method (which will be hereinafter referred to as a xe2x80x9cPWM methodxe2x80x9d) has been known as a method for recording data onto an optical disc at a high density. The PWM method serves to perform modulation such that the edges of front and rear edges of a recording mark correspond to xe2x80x9c1xe2x80x9d of a digital signal, and can assign more bits into the recording mark having the same length as compared with a pulse position modulation method for performing modulation such that the position of the recording mark corresponds to xe2x80x9c1xe2x80x9d of the digital signal. Therefore, the PWM method is suitable for an enhancement in the density.
In the PWM method, the width of the recording mark has information. Therefore, it is necessary to homogeneously form the recording mark on the front and rear edges without distortion. However, in the case where a long mark is to be particularly recorded by the heat regenerating effects of a recording film by means of the phase change type optical disc or the like, the width of the recording mark in the radial direction is gradually increased toward a latter half portion. In other words, there has been a problem in that the recording mark is distorted like a teardrop. In order to solve the problem, there has been proposed a recording method for forming one recording mark by the irradiation of a plurality of short pulse chain (which has been disclosed Japanese Patent Laid-Open Publication No. 3-185628, for example).
Moreover, there has also been proposed a method for changing and recording pulse positions corresponding to a recording leading edge portion and a recording mark terminating portion in a recording pulse chain are changed and recorded for each mark length/space length of data to be recorded, thereby compensating for a peak shift by a thermal interference between marks and a frequency characteristic obtained during reproduction (which has been disclosed in Japanese Patent Laid-Open Publication No. 7-129959, for example).
The operation for forming the recording mark of good quality by changing the position of the recording pulse as described above is generally referred to as xe2x80x9crecording compensationxe2x80x9d.
In the case where the position of the recording pulse is to be changed for the recording compensation, it is necessary to change the edge position of the recording pulse in a time unit which is much shorter than one channel bit of the record data. Therefore, it is hard to generate the recording pulse by a synchronous circuit using a clock signal having a one-channel bit cycle. Therefore, there has generally been taken such a structure that the position of the recording pulse is changed by signal delay means capable of controlling a delay amount (which has been disclosed in the Japanese Patent Laid-Open Publication No. 7-129959, for example).
In the signal delay means, however, the delay amount is generally changed readily for a change in a source voltage, a temperature or the like. In the case where the change in the delay amount which is obtained by a fluctuation in the source voltage, a fluctuation in the temperature or the like is comparatively small, the quality of the record data is not affected. However, in the case where the change in the delay amount is comparatively great, the position of the recording pulse is shifted from a proper position. Therefore, the recording mark cannot be formed correctly so that recording and reproducing characteristics are deteriorated.
In a conventional optical disc recording device, a delay amount for a specific mark length/space length has been fixedly set and there has no means for correcting the positional shift of the recording pulse which is caused by a fluctuation in a source voltage, a temperature or the like.
The conventional optical disc recording device has had such a structure that separate signal delay means is provided for each pulse portion to individually perform control when a plurality of pulse portions in the recording pulse are to be changed in different delay amounts. For this reason, separate signal delay means are required corresponding to the number of the pulse portions to be changed independently. Consequently, a circuit scale tends to be increased. Furthermore, as the position variable range of the pulse portion is more increased, a delay length to be required for individual signal delay means is more increased so that the circuit scale is more enlarged.
In consideration of the above-mentioned problems, it is an object of the present invention to provide an information recording device and an information recording method which comprises means for eliminating the drawbacks and attain the following objects.
(Object 1) To perform recording with high precision even if an environment such as a fluctuation in a source voltage, a fluctuation in a temperature or the like in a device for recording information on an optical disc is changed.
(Object 2) To implement the position control of a recording pulse with high precision within a wide range in a small circuit scale.
In order to attain the above-mentioned (Object 1), the present invention provides an a information recording device for recording data onto an optical disc by irradiating laser beam having at least two kinds of power values which are modulated according to data to be recorded.
The device comprises a recording pulse generator for generating a recording pulse signal by modulating the data to be recorded and correcting a predetermined edge position of the recording pulse signal by delaying the edge position in a delay section incorporated in the recording pulse generator to output the corrected recording pulse signal, a laser driver for driving a laser while switching a power value according to the recording pulse signal, a delay amount measuring section for measuring a delay amount in the delay section, and a recording pulse position correcting section for correcting the predetermined edge position of the recording pulse based on a result of the measurement of the delay amount in the delay amount measuring section.
The laser driver may comprise a plurality of current sources and a plurality of switches for independently turning on/off the supply of an output current from each of the current sources to the laser. The recording pulse generator may output a plurality of recording pulses to the laser driver to control the turning on/off operation of the switches according to the recording pulses.
The recording pulse generator may include a pulse timing generator for generating a reference pulse signal by modulating the data to be recorded, and a delay amount variable delay section for receiving the reference pulse signal to output a delay pulse capable of changing the delay amount externally.
The delay section of the recording pulse generator may have a plurality of inverter elements having each input and output connected in series and selectors for selecting the output of each of the inverter elements. The recording pulse position correcting section may control selection operation of each selector.
The delay section of the recording pulse generator may have a plurality of buffer elements having each input and output connected in series and selectors for selecting the output of each of the buffer elements. The recording pulse position correcting section may control selection operation of each selector.
The delay section of the recording pulse generator may comprise a voltage-controlled delay element, and the recording pulse position correcting section may control the control voltage of the voltage-controlled delay element to correct the predetermined edge position of the recording pulse.
The delay amount measuring section may measure the delay amount between the input and output of the delay section of the recording pulse generator by using a delay measuring clock signal.
The delay amount measuring section may measure a difference in a delay between two kinds of different outputs of the delay amount of the delay sections provided in the recording pulse generator by using a delay measuring clock signal.
The recording pulse position correcting section may calculate a delay setting value with which the delay amount between the input and output of the delay section in the recording pulse generator is a time of about one channel bit, based on the result of the measurement of the delay amount from the delay amount measuring section, and may correct the predetermined edge position of the recording pulse based on the delay setting value.
The recording pulse position correcting section may calculate a delay set value with which the delay difference between two kinds of outputs having different delay amounts of the delay section in the recording pulse generator is a time of about one channel bit, based on the result of the measurement of the delay amount from the delay amount measuring section, and corrects the predetermined edge position of the recording pulse based on the delay set value.
The recording pulse position correcting section may correct the predetermined edge position of the recording pulse generated by the recording pulse generator to a position which is varied depending on the bit length of a recording mark, a last space length or a last space length.
A method according to the invention is a method for recording data on an optical disc while controlling a laser power by using a recording pulse generated by the recording pulse generator. The method comprises the steps of correcting the edge position of a recording pulse while the data are not recorded, and recording data by using a recording pulse of which edge position is corrected.
An another method according to the invention is a method for recording data on an optical disc while controlling a laser power by using a recording pulse generated by the recording pulse generator. The method comprises the steps of recording data, verifying the recorded data, deciding whether or not an edge position of a recording pulse is to be corrected based on an error status of the recorded data with reference to the result of the verification, and correcting the edge position of the recording pulse only when it is decided that the edge position of the recording pulse is to be corrected based on the result of the decision.
The deciding step may decide whether the edge position of the recording pulse is corrected by reference to the error status of the reproduced data in results of a plurality of verifications previously executed.
The correcting step may measure the delay amount of the delay section in the recording pulse generator, and correct the predetermined edge position of the recording pulse based on the result of the measurement of the delay amount.
The correcting step may include the steps of setting a selection signal value for determining the delay amount of the delay section of the recording pulse generator, reading the result of the measurement of the delay amount for the set selection signal value, calculating by using the result of the measurement of the delay amount, a selection signal value corresponding to a delay amount Tw which is a time equal to one cycle of a clock to be used for the recording pulse generator, and converting a time table related to the edge position of a given recording pulse into a set value table of the selection signal value based on the obtained selection signal value.
The time Tw may be a time corresponding to one channel bit of the record data.
The time table may preferably include time information related to variable position of each edge of the recording pulse. Furthermore, the time table may have individual time information for each mark length of data to be recorded, individual information for each combination of the mark length of the data to be recorded and a last space length, or individual time information for each combination of the mark length of the data to be recorded and a next space length.
The correcting step, in the recording pulse generator including a delay section having a plurality of taps of delay elements, may measure a delay amount for each delay element group including a predetermined number of taps of delay elements, and control the output of the delay section to determine the edge position of the given recording pulse based on the measured delay amount for each delay section group.
The correcting step, in the recording pulse generator including a delay section having a plurality of taps of delay elements, may measure a delay amount for each delay element group comprising delay sections in a predetermined number of taps, calculate a delay profile of the whole delay section based on the measured delay amount for each delay element group, and control the output of the delay section for determining the edge position of the given recording pulse based on the calculated delay profile. The delay profile to be calculated may be a function represented by the same number of polygonal lines as the number of the delay element groups. The correcting step may detect a region where the delay time of the delay section is almost coincident with one cycle of a clock signal, by using the clock signal having a cycle which is equal to or less than a half of the total delay time of the delay section of the recording pulse generator, control the output of the delay section based on the result of the detection, and determine the edge position of the given recording pulse.
In order to attain the above-mentioned (Object 2), a method according to the invention is a method for forming each mark by irradiating power-controlled laser beams on an optical disc according to a recording pulse made of a plurality of pulse chain and for recording data with high precision by suitably controlling a predetermined edge position of the recording pulse. The method comprises the steps of generating a delay clock which is obtained by delaying a recording clock having a Tw/n cycle (Tw is one channel bit of the record data and n is a natural number) used for modulation of record data by a suitably controlled delay amount, and determining the predetermined edge position of the recording pulse by a timing of the delay clock.
An another method according to the invention comprises the steps of generating a delay clock which is obtained by delaying a recording clock having a Twin cycle (Tw is one channel bit of the record data and n is a natural number) used for modulation of record data by a suitably controlled delay amount and a reference axis window signal which is pulse-shaped signal, the reference axis window signal having a time width of at least Tw/n synchronized with a rising edge of the recording clock or the falling edge, and having a variable start position by a time unit of Tw/2n, and determining a predetermined edge position of a recording pulse by timings of the delay clock and the reference axis window signal.
When it is necessary to suitably control the predetermined edge position of the recording pulse within a time range of at least dxc3x97Tw/2n (d and n are a natural number), the reference axis window signal may be controlled in (d+1) kinds of timings with a time unit of Tw/2n.
A further method according to the invention is a method for recording data on an optical disc, comprising the steps of forming one mark by irradiating a laser beam, the laser beam being power-controlled according to a recording pulse obtained by synthesizing at least one of a first pulse, a multi-pulse chain which is a repetitive waveform having a Tw cycle and a last pulse, and suitably controlling at least one of a leading edge position of the first pulse and a trailing edge position of the last pulse, thereby recording data with high precision, the leading edge position of the first pulse being defined based on a relative relationship between the leading edge position and a rising phase of the multi-pulse chain, the trailing edge position of the last pulse being defined based on a relative relationship between the trailing edge position and a rising phase of the multi-pulse chain. The method comprises the steps of a) generating a first pulse reference clock having a Tw/n cycle, a last pulse reference clock having a Tw cycle, a first pulse reference axis window signal and a last pulse reference axis window signal, and b) determining a leading edge position of the first pulse by timings of the first pulse reference clock and the first pulse reference axis window signal, and determining a trailing edge position of the last pulse by timings of the last pulse reference clock and the last pulse reference axis window signal. The first pulse reference clock is obtained by delay-control in a relative time having at least a range of xc2x1Tw/4n (n is natural number) for the rising phase of the multi-pulse chain or a phase with delay by about 180 degrees from the rising phase. The last pulse reference clock is delay-controlled within a time range of xc2x1Tw/4n for the rising phase of the multi-pulse chain or the phase with delay by about 180 degrees from the rising phase. The first pulse reference axis window signal synchronizing with the rising phase of the multi-pulse chain or the phase with delay by about 180 degrees from the rising phase, is a pulse-shaped signal having at least one cycle width of the first pulse reference clock, and has a start position variable by a time unit of Tw/2n. The last pulse reference axis window signal synchronizing with the rising phase of the multi-pulse chain or the phase with delay by about 180 degrees from the rising phase, is a pulse-shaped signal having at least one cycle width of the last pulse reference clock, and has a start position variable by a time unit of Tw/2n.
An another device according to the invention is a device for recording data on an optical disc by irradiating laser beams obtained by switching a power value in response to a recording pulse derived by modulated data to be recorded. The device comprises a recording clock generator for generating a recording clock having a Tw/n cycle, a clock delay section for generating m (m is a natural number) kinds of delay clocks having different delay amounts by delaying the recording clock, a pulse reference signal generator for generating m kinds of pulse reference signals each having at least one cycle width or more of the recording clock, by using the record data and the recording clock, a pulse timing signal generator for generating m kinds of pulse timing signals by associating any one of the m kinds of delay clocks with any one of the m kinds of pulse reference signals, a delay amount controller for controlling the delay amount of the m kinds of delay clocks, and a recording pulse synthesizing section for synthesizing the m kinds of pulse timing signals to obtain recording pulses, whereby m of predetermined edge positions in the recording pulse are made variable.
An another device according to the invention is a device for recording data on an optical disc by irradiating laser beams obtained by switching a power value in response to a recording pulse derived by modulated data to be recorded. The device comprises a recording clock generator for generating a recording clock having a Tw/n cycle (Tw is one channel bit of the data to be recorded, n is a natural number), a clock delay section for generating m (m is a natural number) kinds of delay clocks having different delay amounts by delaying the recording clock, a pulse reference signal generator for generating m kinds of pulse reference signals each having at least one cycle width or more of the recording clock, by using the record data and the recording clock, the pulse reference signal being a pulse shaped signal and capable of changing the start position by a time unit of Tw/2n, a pulse timing signal generator for generating m kinds of pulse timing signals by associating any one of the m kinds of delay clocks with any one of the m kinds of pulse reference signals, a delay amount controller for controlling the delay amount of the m kinds of delay clocks and a timing of the m kinds of pulse reference signals, and a recording pulse synthesizing section for synthesizing the m kinds of pulse timing signals to obtain recording pulses, whereby m of predetermined edge positions in the recording pulse are made variable.
The pulse timing signal generator may comprise m D flip-flops. The m kinds of delay clocks may be connected to clock input terminals of the m D flip-flops respectively, the m kinds of pulse reference signals may be connected to D input terminals of the D flip-flops respectively. Thereby m kinds of pulse timing signals could be retrieved from Q output terminals of the m D flip-flops.
The device may further comprises a delay amount measuring section for measuring the delay amount of the clock delay section, whereby the delay amount controller could control the delay amounts of the m kinds of delay clocks based on the result of the measurement of the delay amount which is obtained by the delay amount measuring section.
An another method according to the invention is a method for recording data on an optical disc while controlling a laser power by using a recording pulse modulated according to record data. The method comprises the steps of detecting a temperature of a device for recording data on the optical disc, deciding a change in the detected temperature, correcting an edge position of a recording pulse only when it is decided that the change in the temperature is equal to or more than predetermined value based on the decision of the change in the temperature and recording data by using the recording pulse having a corrected edge position. The edge position can be corrected based on the supply voltage of the device instead of the temperature of the device.